Electronic equipment involving semiconductive devices are essential for many modern applications. The semiconductive device has experienced rapid growth. Technological advances in materials and design have produced generations of semiconductive devices where each generation has smaller and more complex circuits than the previous generation. In the course of advancement and innovation, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometric size (i.e., the smallest component that can be created using a fabrication process) has decreased. Such advances have increased the complexity of processing and manufacturing semiconductive devices.
Micro-electro mechanical system (MEMS) devices have been recently developed and are also commonly involved in electronic equipment. The MEMS device is micro-sized device, usually in a range from less than 1 micron to several millimeters in size. The MEMS device includes mechanical and electrical features formed by one or more semiconductor manufacturing processes. The MEMS device includes fabrication using semiconductive materials to form mechanical and electrical features. For many applications, MEMS device is electrically connected to external circuitry to form complete MEMS systems. Commonly, the connections are formed by wire bonding. The MEMS device may include a number of elements (e.g., stationary or movable elements) for achieving electro-mechanical functionality. MEMS devices are widely used in various applications. MEMS applications include pressure sensors, printer nozzles, or the like. Moreover, MEMS applications are extended to optical applications, such as movable mirrors, and radio frequency (RF) applications, such as RF switches or the like.
Conventionally, MEMS devices require different pressures in the hermetic cavities. For example, an accelerometer requires an enclosure with greater pressure while a gyroscope or a resonator requires an enclosure with lower pressure. However, these MEMS devices are manufactured in the same bonding process. As a result, these MEMS devices in integrated chips have to operate in the same pressure, which will cause certain limitations and constraints. Therefore, there is a continuous need to modify structure and manufacturing method of the MEMS devices in order to improve the device performance as well as reduce manufacturing cost and processing time.